Extended Release of Bupivacaine from Temperature-responsive Hydrogels Provides Multi-day Analgesia for Postoperative Pain

OBJECTIVE

A local anesthetic that provides analgesia lasting at least three days could significantly improve postoperative pain management. This study evaluated the analgesic efficacy and safety of an extended-release formulation of bupivacaine based on the injectable hydrogel carrier poly(N-isopropylacrylamide-co-dimethylbutyrolactone acrylamide-co-Jeffamine M-1000 acrylamide) (PNDJ).

METHODS

The efficacy of PNDJ containing 4% bupivacaine (SBG004) given by peri-incisional subcutaneous injection (SBG004 SC) or wound filling instillation (SBG004 WF) was evaluated compared to saline, liposomal bupivacaine, bupivacaine collagen sponge, bupivacaine-meloxicam polyorthoester, and bupivacaine HCl in a porcine skin and muscle incision model. Mechanical allodynia was assessed by withdrawal from application of von Frey filaments, and local tolerance was evaluated by histology. Bupivacaine pharmacokinetics for SBG004 SC were measured in rabbits (16.5 mg bupivacaine/kg).

RESULTS

Animals demonstrated less mechanical allodynia at incisions receiving SBG004 SC for up to 96 hours postoperatively. Incisions treated with SBG004 SC tolerated more force without a withdrawal indicative of pain compared to saline for 96 hours, and compared to SBG004 WF and all active controls at 24, 48, and 72 hours except bupivacaine-meloxicam polyorthoester at 72 hours. By 49 days, SBG004 was histologically absent and was replaced with granulation tissue infiltrated with immune cells in some areas. In rabbits, Cmax was 41.6 ± 9.7 ng/mL with t1/2 82.0 ± 35.8 hours (mean ± SD).

CONCLUSIONS

Peri-incisional SBG004 SC provided extended release of bupivacaine sufficient to reduce sensation of incisional pain for 96 hours, in vivo bupivacaine delivery for at least 7 days, and a favorable local and systemic toxicity profile.

Local antimicrobial delivery from temperature-responsive hydrogels reduces incidence of intra-abdominal infection in rats

The objective of this study was to evaluate local antimicrobial delivery from temperature-responsive hydrogels for preventing infection in a rat model of intra-abdominal infection (IAI), and to determine whether delivery of tobramycin and vancomycin in combination is effective against IAI pathogens. Rats received intraperitoneal inoculation of E. coli, rat cecal contents, or cecal contents supplemented with E. coli, and received either no treatment, subcutaneous cefoxitin, or local delivery from hydrogels containing vancomycin, tobramycin, or both antimicrobials. Only the hydrogel with tobramycin and vancomycin significantly increased the infection free-rate compared to no treatment for all inocula (E. coli: 13/17, p < 0.0001; cecal contents: 11/17, p = 0.0013; cecal contents + E. coli: 15/19, p < 0.0001). Additionally, tobramycin and vancomycin displayed no synergy or antagonism against clinical isolates in vitro. Local delivery of tobramycin and vancomycin from temperature-responsive hydrogels provides broad coverage and high antimicrobial concentrations for several hours that may be effective for preventing IAIs.

The Diagnosis and Treatment of Acetabular Bone Loss in Revision Hip Arthroplasty: An International Consensus Symposium

Despite growing evidence supporting the evaluation, classification, and treatment of acetabular bone loss in revision hip replacement, advancements have not been systematically incorporated into a single document, and therefore, a comprehensive review of the treatment of severe acetabular bone loss is needed. The Stavros Niarchos Foundation Complex Joint Reconstruction Center at Hospital for Special Surgery held an Acetabular Bone Loss Symposium on June 21, 2019, to answer the following questions: What are the trends, emerging technologies, and areas of future research related to the evaluation and management of acetabular bone loss in revision hip replacement? What constitutes the optimal workup and management strategies for acetabular bone loss? The 36 international experts convened were divided into groups, each assigned to discuss 1 of 4 topics: (1) preoperative planning and postoperative assessment; (2) implant selection, management of osteolysis, and management of massive bone loss; (3) the treatment challenges of pelvic discontinuity, periprosthetic joint infection, instability, and poor bone biology; and (4) the principles of reconstruction and classification of acetabular bone loss. Each group came to consensus, when possible, based on an extensive literature review. This document provides an overview of these 4 areas, the consensus each group arrived at, and directions for future research.

In vivo evaluation of temperature-responsive antimicrobial-loaded PNIPAAm hydrogels for prevention of surgical site infection

Surgical site infections (SSIs) are a persistent clinical challenge. Local antimicrobial delivery may reduce the risk of SSI by increasing drug concentrations and distribution in vulnerable surgical sites compared to what is achieved using systemic antimicrobial prophylaxis alone. In this work, we describe a comprehensive in vivo evaluation of the safety and efficacy of poly(N-isopropylacrylamide-co-dimethylbutyrolactone acrylamide-co-Jeffamine M-1000 acrylamide) [PNDJ], an injectable temperature-responsive hydrogel carrier for antimicrobial delivery in surgical sites. Biodistribution data indicate that PNDJ is primarily cleared via the liver and kidneys following drug delivery. Antimicrobial-loaded PNDJ was generally well-tolerated locally and systemically when applied in bone, muscle, articulating joints, and intraperitoneal space, although mild renal toxicity consistent with the released antimicrobials was identified at high doses in rats. Dosing of PNDJ at bone-implant interfaces did not affect normal tissue healing and function of orthopedic implants in a transcortical plug model in rabbits and in canine total hip arthroplasty. Finally, PNDJ was effective at preventing recurrence of implant-associated MSSA and MRSA osteomyelitis in rabbits, showing a trend toward outperforming commercially available antimicrobial-loaded bone cement and systemic antimicrobial administration. These studies indicate that antimicrobial-loaded PNDJ hydrogels are well-tolerated and could reduce incidence of SSI in a variety of surgical procedures.

Adjuvant antibiotic-loaded bone cement: Concerns with current use and research to make it work

Antibiotic-loaded bone cement (ALBC) is broadly used to treat orthopaedic infections based on the rationale that high-dose local delivery is essential to eradicate biofilm-associated bacteria. However, ALBC formulations are empirically based on drug susceptibility from routine laboratory testing, which is known to have limited clinical relevance for biofilms. There are also dosing concerns with nonstandardized, surgeon-directed, hand-mixed formulations, which have unknown release kinetics. On the basis of our knowledge of in vivo biofilms, pathogen virulence, safety issues with nonstandardized ALBC formulations, and questions about the cost-effectiveness of ALBC, there is a need to evaluate the evidence for this clinical practice. To this end, thought leaders in the field of musculoskeletal infection (MSKI) met on 1 August 2019 to review and debate published and anecdotal information, which highlighted four major concerns about current ALBC use: (a) substantial lack of level 1 evidence to demonstrate efficacy; (b) ALBC formulations become subtherapeutic following early release, which risks induction of antibiotic resistance, and exacerbated infection from microbial colonization of the carrier; (c) the absence of standardized formulation protocols, and Food and Drug Administration-approved high-dose ALBC products to use following resection in MSKI treatment; and (d) absence of a validated assay to determine the minimum biofilm eradication concentration to predict ALBC efficacy against patient specific micro-organisms. Here, we describe these concerns in detail, and propose areas in need of research.

Bacterial toxins in musculoskeletal infections

Musculoskeletal infections (MSKIs) remain a major health burden in orthopaedics. Bacterial toxins are foundational to pathogenesis in MSKI, but poorly understood by the community of providers that care for patients with MSKI, inducing an international group of microbiologists, infectious diseases specialists, orthopaedic surgeons and biofilm scientists to review the literature in this field to identify key topics and compile the current knowledge on the role of toxins in MSKI, with the goal of illuminating potential impact on biofilm formation and dispersal as well as therapeutic strategies. The group concluded that further research is needed to maximize our understanding of the effect of toxins on MSKIs, including: (i) further research to identify the roles of bacterial toxins in MSKIs, (ii) establish the understanding of the importance of environmental and host factors and in vivo expression of toxins throughout the course of an infection, (iii) establish the principles of drug-ability of antitoxins as antimicrobial agents in MSKIs, (iv) have well-defined metrics of success for antitoxins as antiinfective drugs, (v) design a cocktail of antitoxins against specific pathogens to (a) inhibit biofilm formation and (b) inhibit toxin release. The applicability of antitoxins as potential antimicrobials in the era of rising antibiotic resistance could meet the needs of day-to-day clinicians.

2018 International Consensus Meeting on Musculoskeletal Infection: Research Priorities from the General Assembly Questions

Musculoskeletal infections (MSKI) remain the bane of orthopedic surgery, and result in grievous illness and inordinate costs that threaten healthcare systems. As prevention, diagnosis, and treatment has remained largely unchanged over the last 50 years, a 2nd International Consensus Meeting on Musculoskeletal Infection (ICM 2018, https://icmphilly.com) was completed. Questions pertaining to all areas of MSKI were extensively researched to prepare recommendations, which were discussed and voted on by the delegates using the Delphi methodology. The questions, including the General Assembly (GA) results, have been published (GA questions). However, as critical outcomes include: (i) incidence and cost data that substantiate the problems, and (ii) establishment of research priorities; an ICM 2018 research workgroup (RW) was assembled to accomplish these tasks. Here, we present the result of the RW consensus on the current and projected incidence of infection, and the costs per patient, for all orthopedic subspecialties, which range from 0.1% to 30%, and $17,000 to $150,000. The RW also identified the most important research questions. The Delphi methodology was utilized to initially derive four objective criteria to define a subset of the 164 GA questions that are high priority for future research. Thirty-eight questions (23% of all GA questions) achieved the requisite > 70% agreement vote, and are highlighted in this Consensus article within six thematic categories: acute versus chronic infection, host immunity, antibiotics, diagnosis, research caveats, and modifiable factors. Finally, the RW emphasizes that without appropriate funding to address these high priority research questions, a 3rd ICM on MSKI to address similar issues at greater cost is inevitable.

2018 international consensus meeting on musculoskeletal infection: Summary from the biofilm workgroup and consensus on biofilm related musculoskeletal infections

Biofilm-associated implant-related bone and joint infections are clinically important due to the extensive morbidity, cost of care and socioeconomic burden that they cause. Research in the field of biofilms has expanded in the past two decades, however, there is still an immense knowledge gap related to many clinical challenges of these biofilm-associated infections. This subject was assigned to the Biofilm Workgroup during the second International Consensus Meeting on Musculoskeletal Infection held in Philadelphia USA (ICM 2018) (https://icmphilly.com). The main objective of the Biofilm Workgroup was to prepare a consensus document based on a review of the literature, prepared responses, discussion, and vote on thirteen biofilm related questions. The Workgroup commenced discussing and refining responses prepared before the meeting on day one using Delphi methodology, followed by a tally of responses using an anonymized voting system on the second day of ICM 2018. The Working group derived consensus on information about biofilms deemed relevant to clinical practice, pertaining to: (1) surface modifications to prevent/inhibit biofilm formation; (2) therapies to prevent and treat biofilm infections; (3) polymicrobial biofilms; (4) diagnostics to detect active and dormant biofilm in patients; (5) methods to establish minimal biofilm eradication concentration for biofilm bacteria; and (6) novel anti-infectives that are effective against biofilm bacteria. It was also noted that biomedical research funding agencies and the pharmaceutical industry should recognize these areas as priorities. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

Liposomal Formulation Decreases Toxicity of Amphotericin B In Vitro and In Vivo

BACKGROUND

Liposomal amphotericin B is locally delivered to treat fungal orthopaedic infections but little is known about local tissue toxicity, if any, that might be associated with local delivery.

QUESTIONS/PURPOSES

(1) Is liposomal amphotericin B cytotoxic in vitro? (2) Is locally delivered liposomal amphotericin B toxic to tissue in vivo?

METHODS

Mouse fibroblasts (BA LB/3T3 A31) and osteoblasts (MC3T3) were exposed to two formulations of amphotericin B (liposomal and deoxycholate) at concentrations of 0, 1, 5, 10, 100, 500, and 1000 μg/mL. Cell viability was determined by MTT assay after 1, 3, and 5 hours of exposure and a proliferation assay after 1, 4, and 7 days of exposure and then after 3 recovery days without drug. Tissue exposure occurred by local delivery of liposomal amphotericin B, 200 or 800 mg/batch antifungal-loaded bone cement (ALBC), or amphotericin B deoxycholate, 800 mg/batch ALBC in rat paraspinal muscles. White blood cell count (WBC) and serum amphotericin B levels were obtained on Days 1 and 3. Rats were euthanized at 2 and 4 weeks and semiqualitative histopathology was performed.

RESULTS

Liposomal amphotericin B is cytotoxic in vitro but not toxic to tissues in vivo. All cells survived concentrations up to 1000 μg/mL for 5 hours, 100% ± 0%, but none survived ≥ 100 μg/mL for 7 days, 0% ± 0%. Fibrosis was seen adjacent to ALBC without inflammation or necrosis, indistinguishable from controls for both liposomal amphotericin B doses. Amphotericin B serum levels were all less than 1 µg/mL and WBC counts were all normal.

CONCLUSIONS

In vitro cytotoxicity to liposomal amphotericin B occurred but no adverse tissue reaction was seen in vivo.

CLINICAL RELEVANCE

Local delivery of liposomal amphotericin B in ALBC was well tolerated by mouse tissue; however, clinical studies are needed to confirm this finding in humans.

Voriconazole is delivered from antifungal-loaded bone cement

BACKGROUND

Local delivery of antifungals is an important modality in managing orthopaedic fungal infection. Voriconazole is a powder antifungal suitable for addition to bone cement that is released from bone cement but the mechanical properties of antimicrobial-loaded bone cement (ALBC) made with voriconazole are unknown.

QUESTIONS/PURPOSES

(1) Is voriconazole release dose-dependent? (2) Is released voriconazole active? (3) Is the loss of ALBC's compressive strength caused by voriconazole dose- and elution-dependent?

METHODS

Sixty standard test cylinders were fabricated with ALBC: 300 or 600 mg voriconazole per batch eluted for 30 days in deionized water. Voriconizole concentration in the eluate was measured using high-performance liquid chromatography. Cumulative-released voriconizole was calculated. Biologic activity was tested. Compressive strength was measured before and after elution. The effect of dose and time on release and compressive strength were analyzed using repeated-measure analysis of variance.

RESULTS

Fifty-seven percent and 63% of the loaded voriconazole were released by Day 30 for the 300-mg and 600-mg formulations, respectively. The released voriconazole was active on bioassay. Compressive strength was reduced from 79 MPa to 53 MPa and 69 MPa to 31 MPa by 30 days for the 300-mg and 600-mg formulations, respectively.

CONCLUSIONS

Voriconazole release from ALBC increases with dose and is bioactive. Loss in compressive strength is greater after elution and with higher dose.

CLINICAL RELEVANCE

Three hundred milligrams of voriconazole in ALBC would be expected to deliver meaningful amounts of active drug in vivo. The compressive strength of ALBC with 600 mg voriconazole is less than expected compared to commonly used antibacterials.

Jeannette Wilkins Award: Can locally delivered gadolinium be visualized on MRI? A pilot study

BACKGROUND

Management of orthopaedic infections relies on débridement and local delivery of antimicrobials; however, the distribution and concentration of locally delivered antimicrobials in postdébridement surgical sites is unknown. Gadolinium-DTPA (Gd-DTPA) has been proposed as an imaging surrogate for antimicrobials because it is similar in size and diffusion coefficient to gentamicin.

QUESTIONS/PURPOSES

Is in vivo distribution of locally delivered Gd-DTPA (1) visible on MRI; (2) reliably visualized by different observers; (3) affected by the anatomic delivery site; and (4) affected by the in vitro release rate from the delivery vehicle?

METHODS

Twenty-four local delivery depots were imaged in nine rabbits using two anatomic sites (intramedullary canal, quadriceps) with Gd-DTPA in intermediate-porosity polymethylmethacrylate (PMMA) or high-porosity PMMA; six of the nine rabbits also had Gd-DTPA delivered in collagen at a third site (hamstring). A total of 45,000 fat-suppressed T1-weighted RARE scans were acquired using a 7-T Bruker Biospec MRI: nine rabbits, 2-mm slices over 10 cm, four TR values, 25 time periods (pre, every 15 minutes for 6 hours). T1 maps were constructed at every time period. Gd-DTPA distribution was observed qualitatively on the T1 maps. Interobserver reliability was determined.

RESULTS

Locally delivered Gd-DTPA was visible. Interobserver agreement was excellent. Intramuscular delivery followed intermuscular planes; intramedullary delivery was contained within the canal by bone. Distribution from collagen decreased after 1 hour but from PMMA increased over 6 hours.

CONCLUSIONS

Locally delivered Gd-DTPA can be visualized on MRI; distribution is affected by anatomical location and delivery vehicle.

CLINICAL RELEVANCE

Contrast-based imaging using locally delivered Gd-DTPA may be useful as an antibiotic surrogate to determine antibiotic distribution in surgical sites.

Liposomal formulation increases local delivery of amphotericin from bone cement: a pilot study

BACKGROUND

Amphotericin is a highly toxic hydrophobic antifungal. Delivery of amphotericin from antifungal-loaded bone cement (ALBC) is much lower than would be expected for an equivalent load of water-soluble antibacterials. Lipid formulations have been developed to decrease amphotericin toxicity. It is unknown how lipid formulations affect amphotericin release and compressive strength of amphotericin ALBC.

QUESTIONS/PURPOSES

We asked if amphotericin release from liposomal amphotericin ALBC (1) changed with amphotericin load; (2) differed from release from amphotericin deoxycholate ALBC; (3) was an active drug; and (4) if liposomal amphotericin affected the bone cement strength.

METHODS

Forty-five standardized test cylinders were fabricated from three formulations of ALBC: Simplex™ P bone cement with 200 mg liposomal amphotericin, 800 mg liposomal amphotericin, or 800 mg amphotericin deoxycholate per batch. For each ALBC formulation, cumulative released amphotericin was determined from five cylinders, and compressive strength was measured for 10 cylinders, five before elution and five after. Activity of released amphotericin was determined by growth inhibition assay.

RESULTS

Amphotericin release was greater for increased load of liposomal amphotericin: 770 μg for 800 mg versus 118 μg for 200 mg. Amphotericin release was greater from liposomal ALBC than from deoxycholate ALBC: 770 μg versus 23 μg over 7 days for 800 mg amphotericin. Released amphotericin was active. Compressive strength of liposomal ALBC is decreased, 67 MPa and 34 MPa by Day 7 in elution for the 200-mg and 800-mg formulations, respectively.

CONCLUSIONS

Liposomal amphotericin has greater amphotericin release from ALBC than amphotericin deoxycholate. Compressive strength of liposomal amphotericin ALBC decreases to less than recommended for implant fixation. Local toxicity data are needed before liposomal amphotericin ALBC can be used clinically.

Surfactant-stabilized emulsion increases gentamicin elution from bone cement

BACKGROUND

Liquid antimicrobial use for antimicrobial-loaded bone cement is limited because of decreased strength and small volume that can be loaded. Emulsifying the liquid antimicrobial into the monomer may address both issues.

QUESTIONS/PURPOSES

We determined the effect of using a surfactant-stabilized emulsion on antimicrobial release, compressive strength, and porosity.

METHODS

We made 144 standardized test cylinders from emulsified antimicrobial-loaded bone cement (three batches, 72 cylinders) and control antimicrobial-loaded bone cement made with antimicrobial powder (three batches, 72 cylinders). For each formulation, five specimens per batch (n = 15) were eluted in infinite sink conditions over 30 days for gentamicin delivery; five specimens per batch were axially compressed to failure after elution of 0, 1, and 30 days (n = 45); and two noneluted specimens and two gentamicin delivery specimens from each batch (n = 12) were examined under scanning electron microscopy for porosity. Antimicrobial release and compressive strength were compared across cement type and time using repeated-measures ANOVA.

RESULTS

Emulsified antimicrobial-loaded bone cement released four times more antimicrobial than control. Compressive strength of emulsified antimicrobial-loaded bone cement was less than control before elution (58.1 versus 81.3 MPa) but did not decrease over time in elution. Compressive strength of control antimicrobial-loaded bone cement decreased over 30 days in elution (81.3 versus 73.9 MPa) but remained stronger than emulsified antimicrobial-loaded bone cement. Porosity was homogeneous, with pores ranging around 50 μm.

CONCLUSIONS

Emulsified antimicrobial-loaded bone cement has homogeneous porosity with increased drug release but a large loss of strength.

CLINICAL RELEVANCE

Liquid antimicrobials are released from emulsified antimicrobial-loaded bone cement, but increased strength is needed before this method can be used for implant fixation.

Amphotericin B delivery from bone cement increases with porosity but strength decreases

BACKGROUND

Amphotericin B is a highly hydrophobic antifungal used for orthopaedic infections. There is disagreement about whether amphotericin B is released when it is loaded in polymethylmethacrylate (PMMA). It is unknown how much a poragen will increase amphotericin B release or decrease the compressive strength of the PMMA.

QUESTIONS/PURPOSES

We therefore measured amphotericin B release and the compressive strength of amphotericin B loaded bone cement with and without adding high-dose poragen.

METHODS

Antifungal-loaded bone cement was formulated with Simplex P cement and 200 mg amphotericin B with and without 10 g cefazolin (poragen) per batch. Twenty standardized test cylinders were eluted in deionized water for each formulation. Cumulative amphotericin B mass and compressive strength were measured. Data were analyzed using repeated-measures analysis of variance.

RESULTS

Antifungal-loaded bone cement (ALBC) with 10 g poragen delivered more amphotericin B than ALBC containing amphotericin B alone by Day 15, 12.76 μg/cylinder (0.5%) versus 1.74 μg/cylinder (0.04%), respectively. With amphotericin B alone, compressive strength was unchanged and compressive strength did not decrease during elution. Adding 10 g poragen to ALBC with 200 mg amphotericin B decreased the compressive strength and compressive strength decreased further during elution, 80, 61, and 46 MPa at 0, 1, and 30 days, respectively.

CONCLUSIONS

Amphotericin B is released in very small amounts from antifungal-loaded bone cement. Release can be increased by adding high-dose poragen, but compressive strength decreases sufficiently to limit its use for implant fixation.

Amphotericin B is cytotoxic at locally delivered concentrations

BACKGROUND

Orthopaedic fungal infections are commonly treated with systemic amphotericin, which has a narrow therapeutic index and is associated with systemic toxicities. Local delivery of amphotericin has been described yet is poorly understood. As with bacterial infections, fungal infections are associated with biofilm. However, it is unclear whether experience with local delivery of antibacterials can be applied to local antifungal delivery.

QUESTIONS/PURPOSES

We asked whether (1) 100 to 1000 μg amphotericin/mL caused osteoblast cell death; (2) 1 to 10 μg amphotericin/mL caused sublethal toxicity to osteoblasts and fibroblasts; and (3) sublethal amphotericin toxicity could be reversed.

METHODS

Mouse osteoblasts and fibroblasts were exposed in vitro to amphotericin concentrations of 0, 1, 10, 100, and 1000 μg/mL for 5 hours or 0, 1, 5, and 10 μg/mL for 7 days and then 3 days with no amphotericin. Cell morphology on light microscopy and proliferation assays (alamarBlue(®) and MTT) were used as measures of toxicity.

RESULTS

Amphotericin concentrations of 100 μg/mL and above caused cell death; 5 to 10 μg/mL caused abnormal cell morphology and decreased proliferation. Cells regained normal morphology and resumed cell proliferation within 3 days after removal of amphotericin.

CONCLUSIONS

In this in vitro study, amphotericin was cytotoxic to osteoblasts and fibroblasts at concentrations achievable by local delivery.

CLINICAL RELEVANCE

If local concentrations of 100 to 1000 times the minimum inhibitory concentration are necessary to treat biofilm-associated fungal infections as they are for bacterial infection, cell toxicity at the local depot site should be considered.

Hand-mixed and premixed antibiotic-loaded bone cement have similar homogeneity

Since low-dose antibiotic-loaded bone cement (ALBC) was approved by the FDA for second-stage reimplantation after infected arthroplasties in 2003, commercially premixed low-dose ALBC has become available in the United States. However, surgeons continue to mix ALBC by hand. We presumed hand-mixed ALBC was not as homogeneous as commercially premixed ALBC. We assessed homogeneity by determining the variation in antibiotic elution by location in a batch, from premixed and hand-mixed formulations of low-dose ALBC. Four hand-mixed methodologies were used: (1) suspension--antibiotic powder in the liquid monomer; (2) no-mix--antibiotic powder added but not mixed with the polymer powder before adding monomer; (3) hand-stirred--antibiotic powder stirred into the polymer powder before the monomer was added; and (4) bowl-mix--antibiotic powder mixed into polymer powder using a commercial mixing bowl before the monomer was added. Antibiotic elution was measured using the Kirby-Bauer bioassay. None of the mixing methods had consistently dissimilar homogeneity of antibiotic distribution from the others. Based upon our data we conclude hand-mixed low-dose ALBC is not less homogeneous than commercially premixed formulations.

Generic tobramycin elutes from bone cement faster than proprietary tobramycin

Elution of antibiotics from antibiotic-loaded polymethylmethacrylate (AL-PMMA) increases when soluble particulate filler is added to increase the permeability of the PMMA. Antibiotic powder is in itself soluble particulate filler. For greater volume fractions of filler, greater elution occurs. The volume of generic tobramycin powder is more than 3.5 times the volume of proprietary tobramycin powder for a 1.2 g dose leading to the question: Does generic tobramycin elute from AL-PMMA faster than proprietary tobramycin? We performed elution studies on AL-PMMA beads made with 1.2 g of either generic tobramycin or proprietary tobramycin per batch of PMMA. Generic tobramycin eluted more than two times faster than proprietary tobramycin. The release mechanism started as dissolution-driven zero-order release for the generic bead set but for the proprietary bead set the released mechanism started as anomalous diffusion. The release mechanism progressed to diffusion-driven first-order release in both. The increased volume of the generic tobramycin caused more tobramycin to be available for release. The increased elution of tobramycin associated with the greater volume of generic tobramycin powder could lead to clinically higher levels of tobramycin in wound fluid and local tissues; however, the higher volume of powder could potentially cause greater mechanical compromise of the PMMA.

Sucrose, xylitol, and erythritol increase PMMA permeability for depot antibiotics

Release of antibiotics from antibiotic-loaded PMMA is dependent on its permeability. Loading PMMA with soluble particulate filler has been proposed to increase permeability and antibiotic release for beads and spacers. We therefore assessed particulate sucrose, xylitol, and erythritol as fillers to increase the permeability and elution kinetics of filler-loaded PMMA. Based on lower solubility, we hypothesized that erythritol would not enhance permeability and elution as much as xylitol and sucrose. We made filler-loaded PMMA beads with each of the three fillers combined with phenolphthalein, and soaked in 0.1% NaOH solution. Permeability was assessed qualitatively by relative depth of phenolphthalein color change caused by penetration of NaOH solution into subsequently split beads. Elution was quantitatively assessed by spectrophotometric light absorption measurements of the eluent. Fluid penetration reached the center of 7-mm beads by day 15, similar for all three materials. Elution of phenolphthalein was greater for xylitol than for the other two materials. Particulate sucrose, xylitol, and erythritol fillers increase PMMA permeability and elution kinetics but relative solubility did not determine the relative degree of enhancement of permeability and elution by these materials.

Particle size of fillers affects permeability of polymethylmethacrylate

Particulate soluble filler added to polymethylmethacrylate increases its permeability, leading to increased elution. We asked whether particle size affects permeability and elution rate associated with a given volume fraction of filler. Permeability of filler-loaded PMMA was measured in 9 mm rods with a 32% volume fraction of four particle sizes (106 microm, 212 microm, 425 microm, 850 microm) and two filler materials (sucrose and xylitol) using a modified phenolphthalein-sodium hydroxide technique, which allowed quantitative serial observation on the same specimens. Fluid penetration was faster for larger particle sizes. The elution rate was greater for smaller particle sizes on qualitative visual assessment. Sucrose fillers were not different from xylitol fillers independent of particle size. For the volume fraction of 32%, larger particles lead to larger caliber porosity, less pore interconnectivity, and faster fluid penetration. Smaller size particles lead to smaller caliber porosity, greater pore interconnectivity, smaller areas between the pores with no fluid penetration and greater increase in the effective surface area causing a greater elution rate.

Xylitol and glycine fillers increase permeability of PMMA to enhance elution of daptomycin

The elution of antibiotics from hand mixed antibiotic-laden polymethylmethacrylate (PMMA) must be increased to achieve clinical performance equivalent to commercially manufactured antibiotic beads (not available in the USA) in the management of musculoskeletal infections. Adding fillers such as glycine and dextran to polymethylmethacrylate increases the elution of antibiotics from antibiotic-laden PMMA. We propose xylitol, a naturally occurring sweetener with direct antibiofilm properties, as a filler material. To compare the efficacy of xylitol and glycine as fillers on the elution of antibiotics from PMMA, elution studies were performed on mixtures of Palacos polymethylmethacrylate and daptomycin (1 gm) with xylitol or glycine as the filler (28 g). Xylitol and glycine enhanced the daptomycin activity eluted from the polymethylmethacrylate. Xylitol was more effective than glycine, having a greater increase in daptomycin release at all data points; on day one xylitol increased the elution of daptomycin 2.67 times whereas glycine increased it 1.78 times also on day one. The eluant concentration of daptomycin remained higher longer for xylitol; 3.90 microg/mL for xylitol versus 2.25 microg/mL for glycine on day 9. Xylitol is inexpensive and readily available. It can be hand mixed with PMMA, and is more effective than glycine as a filler to enhance daptomycin release. Considering possible antibiofilm activity, xylitol may be a more advantageous choice.

Phenolphthalein used to assess permeability of antibiotic-laden polymethylmethacrylate: a pilot study

Elution of antibiotics from polymethylmethacrylate laden with antibiotics is dependent on the permeability of the polymethylmethacrylate. Increasing polymethylmethacrylate permeability by adding fillers has been suggested to increase antibiotic elution but the resulting increase in permeability has not been assessed directly. A simple method to assess polymethylmethacrylate permeability is proposed. Phenolphthalein was added to the polymethylmethacrylate to indicate the level of penetration of fluid with pH of 10.3. Glycine in three different amounts (0.45 g, 7 g, and 28 g) or a combination of antibiotics (13.6 g) was added as a filler to increase the permeability. Beads of each mixture were made and soaked in fluid with a pH of 10.3. An immediate intense magenta coloration occurred on contact of the beads with the fluid. A zone of magenta was seen to penetrate into the depths of polymethylmethacrylate beads. That penetration increased with the amount of the filler and with time in the fluid bath. The type of filler material also affected the rate of fluid penetration. Permeability of various antibiotic polymethylmethacrylate mixtures can be determined qualitatively using this method. The observations may be useful to determine which mixtures warrant more expensive antibiotic elution studies.

Is aseptic loosening truly aseptic?

Surgeons who treat osteomyelitis or infected implants think that microorganisms can live on and around implanted biomaterials and necrotic bone without clinical manifestations of infection. Gristina and Costerton, in their seminal work, suggested that such bacteria persist within biofilms and that they are often overlooked when diagnosis is based on standard microbiologic culture techniques. Subsequent studies using specialized techniques including sonication to remove adherent bacteria and direct detection using various forms of microscopy have confirmed that bacteria are present in many culture-negative cases. This led to the suggestion that at least some cases of failed orthopaedic implants that were considered aseptic loosening based on the absence of clinical signs of infection and the failure to isolate bacteria may actually have an infectious etiology. In addition to biofilms, potentially important concepts that also may contribute to false-negative culture results include the failure to recognize small colony variants induced during growth in vivo and the presence of bacteria inside host cells including osteoblasts. Importantly, bacteria persisting as small colony variants within biofilms and/or inside osteoblasts also may be an explanation for the recurrent nature of musculoskeletal infection.

The effect of glycine filler on the elution rate of gentamicin from acrylic bone cement: a pilot study

Elution of antibiotics from acrylic bone cement (polymethylmethacrylate [PMMA]) is dependent on the access of fluid to the depths of the cement that contains the antibiotic. Commercially prepared antibiotic beads that are porous have higher elution rates than hand-mixed, nonporous antibiotic PMMA mixtures. To increase the elution of gentamicin from hand-mixed PMMA, glycine was added as a filler to produce porosity. Elution of gentamicin from the antibiotic PMMA-glycine mixture increased with increasing amounts of glycine. With 3.6 g gentamicin powder and 14 g of crystalline glycine per batch of Palacos PMMA, the elution of gentamicin from the PMMA at 2 days was, similar to the previously documented elution of gentamicin from commercially prepared porous Septopal PMMA beads. With further investigation it may be possible to identify a specific filler and a volume of filler that can be hand mixed in antibiotic PMMA to produce the elution behavior that is needed for specific clinical requirements.

Alternative materials to acrylic bone cement for delivery of depot antibiotics in orthopaedic infections

Acrylic bone cement has considerable laboratory and clinical data validating it as a delivery material for depot administration of antibiotics. However, an alternate material that does not require a secondary procedure for removal is desired. Many biodegradable materials have been evaluated as alternatives including protein-based materials (collagen, fibrin, thrombin, clotted blood), bone-graft, bone-graft substitutes and extenders (hydroxyapatite, beta-tricalcium phosphate, calcium sulfate, bioglass), and synthetic polymers (polyhanhydride, polylactide, polyglycolide, polyhydroxybutyrate-co-hydroxyvalerate, polyhydroxyalkanoate). Various forms and combinations of these materials have been investigated worldwide, characterizing their elution properties and performance in treating osteomyelitis in animal models. Many of these have had limited clinical evaluation. Outside the United States, some of these materials are used clinically. In the United States, none have been approved. None are commercially available for clinical use. Morselized cancellous bone and calcium sulfate are the two materials that have been used clinically in the United States on a physician-prescribed, hand-mixed, basis. Considering the limited clinical data that currently are available, the use of these materials still is experimental. Clinical application should be cautious, limiting the total antibiotic load. Until definitive data are available, a prudent dose would be no higher than one that would have acceptable toxicity risk if administered intravenously over 24 hours.

The effect of sampling method on the elution of tobramycin from calcium sulfate

Release rate is a critical property of all drug delivery vehicles, including antibiotic-laden bioerodibles. In vitro elution studies, used to evaluate release rates, use different sampling methods, including changing the entire amount of buffer and partial exchanges each day. Two groups of 10% calcium sulfate-tobramycin pellets were eluted in 20 mL of buffer for 30 days. Group I had 5 mL of buffer withdrawn and replaced daily whereas Group II had the entire 20 mL of buffer changed daily. The results show that the complete exchange method caused a significantly faster release of antibiotic than the partial exchange method. In the complete exchange group, greater than 50% of the tobramycin was released by 24 hours, whereas in the partial exchange group, 50% of the antibiotic was not released until Day 6. The two methods of sampling used to evaluate this bioerodible material provide data that allow the user to anticipate how the material will function in relatively inert and volatile environments. The method used to sample the elution of antibiotics from bioerodible materials affects the amount of antibiotic eluted. It therefore is important to know the method of sampling when making a decision to use a bioerodible material to deliver antibiotics locally.

Salvage of infected total knee components

Debridement and retention of components for the treatment of infected total knee replacements has not been effective, with a failure rate of more than 70%. In cases where there are solidly fixed components, particularly with long stems, a method of successfully retaining the components is desirable. A protocol of radical debridement has been developed to eradicate the biofilm related bacteria associated with these infections. Assessment of the interfaces and elimination of all spaces and unsealed interfaces that will allow penetration by bacteria is essential. Four cases of infected total knee replacements are reported without recurrence after a minimum of 18 months. Refinement of the protocol and longer followup on more cases is planned to validate the early results.

Open reduction internal fixation of supracondylar fractures above total knee arthroplasties using the intramedullary supracondylar rod

Seven patients who had low supracondylar fractures above total knee arthroplasties were treated using the intramedullary supracondylar rod. Six of the seven patients were steroid-dependent, long-standing severe polyarticular rheumatoid arthritics with marked osteopenia. The intramedullary supracondylar rod provided stable fixation that allowed early range of motion of the knee. Union occurred in good position in all patients; return to prefracture function was achieved in three months. The surgical procedure was reliable and was associated with minimal morbidity.

Arthroscopic débridement of the knee for osteoarthrosis

To evaluate outcome after arthroscopic débridement, the records of 171 patients with osteoarthrosis of the knee were reviewed. All patients were unresponsive to conservative management and were treated arthroscopically. Procedures included lavage, meniscectomy, chondrectomy, removal of free bodies and removal of limited osteophytes. Outcome assessment was retrospective, evaluating the need for further surgery, control of pain, improved function and patient satisfaction. Sixty-five percent of patients felt their symptoms were improved. There was excellent control of pain in 38% and improved function in 22%. Subsequent surgical procedures were required in 12% at an average follow-up of 25 months. No factors were identified that correlated with the outcome, including the extent of degenerative changes and of débridement and patient profile. Arthroscopic débridement is a temporizing procedure with good patient satisfaction. Marked, but unpredictable, improvement in symptoms is seen in one patient out of three.

Locked intramedullary fixation for metaphyseal malunion and nonunion

Locked intramedullary rod fixation, established for metaphyseal fractures, is applicable to reconstructive procedures. Fourteen cases of complex nonunion or malunion (five infected) were reviewed retrospectively. Thirteen of the 14 fractures united. Eleven of 14 required an open procedure for removal of metal, soft-tissue release, bone grafting, osteotomy, or resection of infected bone. Infections were controlled by resection, depot antibiotics, and early stabilization. Interlocking intramedullary rods are an excellent fixation technique for posttraumatic metaphyseal reconstructive procedures.

Long-term pain and disability in relation to residual deformity after displaced pelvic ring fractures

In a retrospective review and follow-up study of 43 patients who had had high-energy pelvic fractures 5 or more years earlier, the occurrence of late pain and the functional outcome were adversely related to residual deformity of the pelvic ring. Among patients who had no residual deformity (displacement less than 1 cm), 88% had no serious pain and 82% had normal function. Of patients who had residual deformity (displacement more than 1 cm posteriorly), only 30% had no serious pain (p less than 0.01) and only 30% had normal function (p less than 0.01). Definitive reduction and stabilization is therefore recommended early after the injury whenever possible.

Intramedullary rod fixation of femoral shaft fractures: comparison of open and closed insertion techniques

Meta-analysis of published series of intramedullary rod fixation in fractured femurs revealed significantly higher union rates, lower deep infection rates and a better range of knee motion when closed rather than open techniques of insertion were used. A separate retrospective review of 58 femoral fractures at one hospital showed outcomes consistent with those reported in the literature; these results were obtained during a 6-year period when staff were learning closed techniques. Technical failures of the closed technique can be avoided by paying attention to well-established operative details. A system for grading outcomes was developed to compare objectively the results of treatment of fracture patients. The literature and the authors' experience support the adoption of closed techniques for intramedullary rod insertion in femoral shaft fractures.

Analysis of radionuclide arthrograms, radiographic arthrograms, and sequential plain radiographs in the assessment of painful hip arthroplasty

An analysis of sequential plain radiographs (XR), radionuclide arthrography, (RNA), and radiographic arthrography (RGA) was performed to determine the efficacy and usefulness of each study in the diagnosis of loosening of prosthetic hip components. Over a 2-year-period, 65 hip prostheses were assessed before operation using each type of study; these results were compared to the intraoperative assessment of the status of the components. Of the three studies, sequential plain radiographs were overall the most accurate, sensitive, and specific. Radionuclide arthrography was of no use on the acetabular side but quite useful on the femoral side, especially in cases with only minimal femoral component loosening. Radiographic arthrography was overall the least accurate or sensitive of the three studies performed.

Prophylaxis with indomethacin for heterotopic bone. After open reduction of fractures of the acetabulum

Forty-four fractures of the acetabulum that had been treated with open reduction and internal fixation necessitating dissection of the gluteal muscles were reviewed radiographically for the development of heterotopic bone. Grade-2 (Brooker classification) or more severe heterotopic ossification was seen in thirteen (50 per cent) of twenty-six patients who did not receive indomethacin but in only one (5.5 per cent) of eighteen patients who received indomethacin for six weeks postoperatively. In the patients who did not receive indomethacin, the maximum amount and extent of the heterotopic bone was evident in twelve weeks. In the patients who did receive indomethacin, the heterotopic ossification did not progress after the administration of indomethacin was discontinued. We concluded that, in patients who have a fracture of the acetabulum, indomethacin provides effective prophylaxis for heterotopic bone after operative reduction with gluteal dissection.

Anterolateral compression fracture of the thoracolumbar spine. A seat belt injury

A thoracolumbar injury is reported in four patients who were involved in motor vehicle accidents while wearing shoulder-lap belt assemblies. These injuries consisted of anterolateral wedge compression of a thoracolumbar vertebra with lateral compression occurring on the side opposite the restrained shoulder. The posterior elements were disrupted contralateral to the anterolateral body compression. There was no translation in any of these fractures, and there were no neurological injuries. All fractures united without significant late disability. Although there was no gross clinical instability in these fractures, two of the three columns of the spine are disrupted, suggesting potential instability. The postulated mechanism of injury, referred to as the roll-out phenomenon, is flexion and rotation about the axis of the shoulder strap.

Longitudinal stress fracture of the tibia: case report

Stress fractures usually present with vague clinical features and delayed radiographic findings. A patient with a longitudinal stress fracture of the tibia is described here. Computed tomographic images, perpendicular to the fracture, were diagnostic while plain radiographs and scintigraphy showed nondiagnostic changes due to an unexpected fracture pattern.

Biceps tendon blocks reduction of isolated radial head dislocation

A case of an unreducible radial head dislocation found in a 7-year-old girl illustrates the frequent delay in diagnosis associated with radial head dislocation. Her initial radiographs showed the radial neck access not passing through the center of the capitulum, which is diagnostic of radial head dislocation. She had no associated injuries to the elbow joint or neurovascular structures. Closed reduction was not stable, and open reduction revealed the biceps tendon displaced posteriorly and laterally from the radial tubercle around the radial neck, which prevented stable reduction of the anteromedial dislocation of the radial head. Once it was reduced through the radial capitular joint to its normal anatomy, the reduction was stable. Following a routine postoperative course, an excellent result was obtained.

Cauda equina syndrome: a complication of lumbar discectomy

Six cases of acute postdiscectomy cauda equina syndrome (C.E.S.) following lumbar discectomy were reviewed retrospectively in a series of 2842 lumbar discectomies over a ten-year period. Five cases had coexisting bony spinal stenosis at the level of the disc protrusion. The bony spinal stenosis was not decompressed at the time of discectomy. Inadequate decompression played a role in the neurologic deterioration postoperation. The cause of the sixth case is unknown. Bowel and bladder recovery was good when the cauda equina decompressed early; sensory recovery was universally good, and motor recovery was poor if a severe deficit had developed before decompression. Careful review of the preoperative myelogram to rule out spinal stenosis and decompression of bony stenosis at discectomy are recommended for prevention of postoperative C.E.S. Urgent decompression of postoperative C.E.S. is advisable if compression of the cauda equina is confirmed radiographically.

The pressure distribution under tourniquets

We measured the detailed pressure distribution under pneumatic tourniquets and Esmarch bandages in canine limbs. The results showed that pressure concentration can occur in the tissue under the tourniquet. The Esmarch-bandage tourniquet was shown to be capable of producing pressures in excess of 1000 millimeters of mercury immediately beneath the tourniquet. There is a wide variation between cuff pressure and the pressures in the underlying tissues.

A Transmission Electron Microscope Study of Amethyst and Citrine

Thin crystals of amethyst and citrine were examined by transmission elflf'troJl microscopy. It was found that all crystals became damaged during observflti"ll. The diffraction contrast from the damage centres indicated that these were RmfLll amorphous regions. Electron spin resonance observations of these crystals show that the amorphous regions are associated with Fe3+ ions; the damage centres provide, therefore, a measure of the distribution of this impurity in the crystals. Brazil twin boundaries, generally of the order of 1000 A apart, were observed directly. Radiation damage occurred preferentially at the twin boundaries suggesting that there was a concentration of impurities along them. The relevance of these observations to the optical properties of the crystals is discussed briefly.

Dislocation Substructures in Deformed and Recovered Chromium

In an attempt to correlate the degree of plastic deformation of chromium with the physical properties associated with its antiferromagnetism, a study has been made by thin-foil electron microscopy of the dislocation substructures in polycrystalline chromium sheet after deformation by rolling and subsequent annealing. The original hot-rolled sheet exhibited a typical cell structure.